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Bollettino di Geofisica Teorica ed Applicata Vol. 55, n. 2, pp. 389-404; June 2014 DOI 10.4430/bgta0096 Historical seismicity of the Kyparissiakos Gulf, western Peloponnese, Greece G.A. PAPADOPOULOS, I. BASKOUTAS and A. FOKAEFS Institute of Geodynamics, National Observatory of Athens, Greece (Received: January 8, 2013; accepted: April 2, 2013) ABSTRACT The historical seismicity of the Kyparissiakos Gulf, western Peloponnese, Greece, is reviewed covering the time period from the 5th century B.C. up to A.D. 1910. Previous earthquake catalogues and other studies, little known seismological archives and archaeological reports were taken into account. A parametric historical catalogue of the area was compiled. Key words: historical earthquakes, Kyparissiakos Gulf, Greece, SEAHELLARC. 1. Introduction The region of the western Peloponnese is characterized by very high seismicity with respect to many other areas of Greece. This is due to that it marks the African-Eurasian plate convergence in the western segment of the Hellenic Arc. The seismicity of the region, which is documented by the record of both instrumental and historical earthquakes, has been of particular interest for the seismic hazard assessment in the area of Pylos town, which was the test-site for the EC-FP6 SEAHELLARC (SEismic and tsunami risk Assessment and mitigation scenarios in the western HELLenic ARC) project (see Papoulia et al., 2014). A preliminary seismic hazard study for the area of Pylos and the surrounding region of south- western Peloponnese was published by Slejko et al. (2010). The earthquake catalogue used in that study was derived from three data files: 1) the historical and early instrumental Greek earthquake catalogue, which covers the period from 550 B.C. to A.D. 1963; 2) the modern Greek instrumental earthquake catalogue, which covers the period from 1964 to 2006; 3) the recent earthquake locations from 2007 to 2010 inclusive. As regards the data sets for the time period from 1911 up to 2010, they were compiled from the earthquake catalogues of the Institute of Geodynamics, National Observatory of Athens (NOA) for the time period 1964 - 2010 and of the Geophysical Laboratory of the University of Thessaloniki for the time period 1911 - 1963. These catalogues are accessible at http://www.gein.noa.gr/el/seismikotita/ katalogoi-seismwn and http://geophysics.geo.auth.gr/ss/, respectively. The historical earthquake catalogue before 1911 was compiled on the basis of the catalogue presented by Papazachos and Papazachou (1997) modified according to the publications of Papadopoulos et al. (2000); Papadopoulos and Plessa (2001); Papadopoulos and Vassilopoulou (2001). However, for the special needs of the seismic hazard assessment in Pylos, a further investigation of historical earthquakes was carried out by us. © 2014 – OGS 389 Boll. Geof. Teor. Appl., 55, 389-404 Papadopoulos et al. In this paper we present the results of the historical seismicity investigation which included not only earthquake events that occurred in the western Peloponnese and were used in the hazard assessement study by SEAHELLARC Working Group (2010) but also events which were reviewed after the publication of that study. From this point of view our results are of interest which goes beyond the research groups that worked for the SEAHELLARC project. Translations of Greek texts to English were prepared by us unless otherwise specified. 2. Historical seismicity revisited Catalogues of the Greek historical seismicity containing information about earthquakes occurring in western Peloponnese include among others Mallet (1853, 1855); Schmidt (1879); Georgiades (1904); Sieberg (1932); Galanopoulos (1961, 1981); Shebalin et al. (1974); Papazachos and Papazachou (1989, 1997, 2003); Guidoboni et al. (1994); Spyropoulos (1997); Ambraseys and Finkel (1999); Guidoboni and Comastri (2005); Ambraseys (2009). In addition, studies focusing closer in the area of interest were published by Galanopoulos (1950). A systematic effort for updating and revising the earthquake catalogue of the Hellenic Arc and trench, including the area of study, can be found in the publications by Papadopoulos and Plessa (2001); Papadopoulos and Vassilopoulou (2001); Papadopoulos (2011). In this section we reexamined the historical seismicity in western Peloponnese from the antiquity up to 1910. Among others we examined little known earthquake events and reassessed earthquake parameters. A summary list of the earthquakes examined is contained in Table 1. Our investigation was based on published catalogues and other earthquake studies, on archaeological reports as well as on little known diaries and earthquake archives, the most important being the systematic and reliable archive organized in NOA for the time period from 1893 to 1915 inclusive [Anonymous (1893-1901, 1902-1915): see more explanations in Papadopoulos et al. (2000)]. The experience from modern Greek seismicity is that the instrumental earthquake epicentre as a rule is placed very close to the area where the maximum seismic intensity is felt. This is valid particularly for shallow earthquakes of no large magnitude, which is the majority of cases examined in this paper. Therefore, this rule was adopted for the earthquake epicentre determination unless it is specified otherwise. Earthquake magnitudes were determined by applying two groups of empirical relationships between surface-wave magnitude, Ms, and seismic intensity, I, developed by Papadopoulos (2011) from a data set of the Greek instrumental seismicity for the time period 1911 - 2005. The first group includes 4 linear relationships between Ms and Imax while the second group includes 18 linear relationships between Ms and log Ai; Ai is the surface of perceptibility area of intensity degree i. For both groups relationships for inland, coastal, offshore and all earthquakes were developed. Inland earthquakes had epicentral distance, Δ, more than 20 km inland from the closest sea-shore, while coastal earthquakes had Δ up to 20 km either inland or offshore from the closest sea-shore. In this paper, the general rule for magnitude calculation is to use one relationship from the first group and at least one from the second group provided that intensity data are available. Intensities are estimated according to the MM (Modified Mercalli) scale. Intensity information can be found in the relevant publications cited separately for each one of the earthquakes 390 Historical seismicity of the Kyparissiakos Gulf Boll. Geof. Teor. Appl., 55, 389-404 Table 1 - Parametric historical earthquake catalogue for the area of the Kyparissiakos Gulf. Key: n. = code number, Mo = month, D = day, H = hour, m = minute, s = second, ϕN = geographic latitude (in degrees and minutes), λΕ = geographic longitude (in degrees and minutes), h = focal depth, n = shallow earthquake, ni = interplate earthquake, i = intermediate-depth earthquake, Im = maximum intensity in MM scale, M = magnitude equivalent to Ms, R = reliability of the earthquake event in a 4-grade scale with 1 representing very uncertain event and 4 representing absolutely certain event, nI = number of intensity points available in the respective references (see text). n. Year Mo D H m s ϕN λE h Im, Site M R nI 1 400 BC 37 36 21 36 n ≥ VI Olympia 6 3 1 2 2ndc.BC n Olympia 3 3 6th c. AD n Filiatra 3 4 1428 5 Methoni, Koroni 3 5 1642 5 30 36 42 22 00 n Koroni 4 1 6 1684 9 Kalamata 3 7 1736 Koroni 3 8 1752 12 25 n Skafidia, Elis 3 9 1796 8 VI-VII Pylos 3 10 1805 4 18 19 30 37 03 22 30 n Kalamata 3 1 11 1834 01 01 Olympia 3 12 1838 11 18 Kalamata 3 13 1841 12 31 Pyrgos 3 14 1842 4 18 09 40 37 06 22 12 n IX Messini 6.3 4 8 0.2 15 1846 6 10 02 00 37 12 22 00 n IX Mikromani 6.2 4 27 0.3 16 1875 4 24 37 18 21 42 n VII-VIII 6.0 4 1 Kyparissia 0.1 17 1885 3 28 18 23 37 09 21 54 n VIII-IX 6.0 4 8 Messini 0.2 18 1886 8 27 21 32 37 06 21 42 ni IX-X 6.8 4 126 Filiatra 0.3 19 1887 3 5 22 37 12 21 42 n V-VI 5.5 3 2 Kalamata 0.1 20 1894 7 26 37 42 21 42 n VI-VII 5.7 3 1 Douka, Elis 0.2 21 1896 12 28 23 30 n VII Jannitsa 5.5 4 4 0.2 22 1898 11 9 18 15 37 18 21 42 n VII Kyparissia 5.6 4 9 0.2 23 1899 1 22 7 50 37 12 21 42 n IX Kyparissia 6.1 4 25 0.2 24 1903 8 11 4 32 54 36 12 23 24 i IX-X Mitata 6.6 4 262 Kythira 0.2 25 1909 3 8 15 55 37 42 21 12 n VII Katakolo 5.5 4 6 0.3 26 1909 7 15 0 28 37 54 21 30 n VIII-IX Chavari 6.0 4 10 0.2 27 1910 12 27 3 54 30 37 54 21 12 n VII-VIII 5.7 4 2 Lechaina 0.2 391 Boll. Geof. Teor. Appl., 55, 389-404 Papadopoulos et al. examined. The earthquakes of 1875, 1887, 1894, 1899 and of July 15, 1909 were taken as examples and their magnitude calculation is analysed in next lines after the descriptions of these earthquakes. For a few events, however, earthquake magnitude or epicentral coordinates were adopted from other authors. The three empirical formulas applied here are the next: M = (4.12471 ± 0.25587) + (0.24996 ± 0.0328) Imax, coastal (1) M = (3.36678 ± 0.50747) + (0.3345 ± 0.05995) Imax, inland (2) M = (3.79929 ± 0.24227) + (0.63188 ± 0.06547) (log AV), coastal (3) where M is surface-wave magnitude, Imax= maximum seismic intensity, AV = surface of the area (in km2) covered by the isoseismal of degree V.